There exist systems for performing combined phoropter and refractive measurements to ascertain the aberrations present in the eye of a subject. One such system is described in International Patent Publication No. WO/2013/150513, for “Objective Phoropter System” having common inventors with the present application, and co-assigned with the present application. That system uses a pair of phoropter wheel assemblies, one for each eye, each assembly comprising a number of lens wheels incorporating the series of lenses and wedges required to compensate for a wide range of refractive aberrations in the vision of the eye being tested. The vision of each eye is corrected by a combination of a subjective phoropter measurement, iteratively performed with an objective wavefront analysis measurement to determine the residual aberrations existing after the initial phoropter correction. The wavefront analysis measurement can be performed by any of the known methods, and particularly by the use of a Shack-Hartmann array to analyze the deviation of the retinal reflected wavefront from a planar wave, as is known in the art.
However, there are a number of shortcomings with such prior art systems. In the first place, the accuracy of the systems rely on the nominal values of the lenses used in the lens wheels, such that if any of the lenses have an inaccurate value, the supposed optical power of the lens combination used will be incorrect, and the prescription output for preparing correction spectacle lenses will be inaccurate. Such inaccuracy can also arise because of poor alignment of the lens wheels. As a result, the vision correction prescription will not provide the optimum correction possible for the subject.
Additionally, the subject's eyes may not be positioned at the correct distance from the phoropter lens wheels, and since this distance is important for prescribing lenses which will provide optimum correction in a spectacle frame which is designed to sit at a standard distance from the user's eyes, any deviation therefrom will result in less than optimum vision correction. Therefore, a more accurate method of ensuring the correct focal position of the eye relative to the phoropter lens wheels also needs to be provided. The same consideration applies to the lateral centering of the subject's eyes during the measurements, and prior art methods using the pupil image to center the eye during the measurements may not be optimal.
There therefore exists a need for an objective phoropter instrument which overcomes at least some of the disadvantages of prior art systems and methods.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.